We propose to identify cell surface molecules which are critical to cell and tissue differentiation in both preimplantation and postimplantation mouse embryos. A number of stage specific polypeptides unique to zygotes and 2 cell embryos, to 4-8 cell embryos, and to early blastocysts have been identified. Monoclonal antibody to these stage specific polypeptides will be produced by immunization of rats with embryos, followed by somatic cell fusion of rat spleen cells with transplantable mouse myeloma tumor cells. In parallel experiments, teratocarcinomas will be induced from homozygous t/t mutant embryos. Monoclonal antibody will be produced against muring teratocarcinoma cells. The antibodies identified by these techniques will be used to study stage specific polypeptides and teratocarcinoma antigens, to define their localization (intracellular or cell surface) and to attempt to define their functions. Preliminary biochemical characterization of cell surface polypeptides involved in early mouse development will be carried out by immunprecipitation and gel electrophoresis. Several t mutants will be st@died by the method of tetraparental mouse production to determine if they are in fact cells lethals or not. The tissue distribution of antigens recognized by the monoclonal antibodies described above will be determined, and preliminary functional studies will be carried out.